The present invention relates to a substrate processing method and apparatus for mainly mass-producing SOI substrates having uniform quality and, more specifically, forming porous silicon used to manufacture SOI substrates, and an SOI substrate.
Porous silicon was found by A. Uhlir and D. R. Turner who were studying electropolishing of single-crystal silicon biased to a positive potential in an aqueous solution of hydrofluoric acid (to be abbreviated as xe2x80x9cfluoric acidxe2x80x9d hereinafter).
Later, to exploit the excellent reactivity of porous silicon, application to element isolation in which a thick insulating structure need be formed in manufacturing a silicon integrated circuit was examined, and a full isolation technology using a porous silicon oxide film (FIPOS: Full Isolation by Porous Oxidized Silicon) was developed (K. Imai, Solid State Electron 24, 159, 1981). This is the first example of application of porous silicon to the SOI (Silicon On Insulator) technology.
Recently, an applied technology to direct bonding in which a silicon epitaxial layer grown on a porous silicon substrate is bonded to an amorphous substrate or single-crystal silicon substrate via an oxide film has been developed (Japanese Patent Laid-Open No. 5-21338).
Details of this technology will be described below. First, a first substrate is etched in an electrolytic solution represented by HF solution to form a porous silicon layer on the surface of the substrate. A single-crystal silicon film is epitaxially grown on the porous silicon layer. This layer is grown as a non-porous single-crystal thin film although the underlying layer is porous. Subsequently, the surface of the epitaxial layer is oxidized. After cleaning, the oxide film surface and a second substrate are bonded and integrated by a heat treatment. The resultant structure is ground from the lower surface side of the first substrate to expose the porous layer. Finally, the porous silicon layer exposed to the surface is removed by etching while leaving the single-crystal silicon film, thereby obtaining a substrate having an SOI structure.
Conventionally, however, when the porous silicon layer is removed by etching, the porous silicon layer partially remains on the single-crystal silicon film.
The present invention has been made to solve the above problem, and has as its object to provide a substrate processing method and apparatus capable of satisfactory etching in the process of removing a porous silicon layer by etching.
It is another object of the present invention to provide an SOI substrate manufactured by the above processing method and apparatus.
In order to solve the above problem and achieve the above objects, a substrate processing method according to the first aspect of the present invention has the following steps.
There is provided a substrate processing method comprising the anodizing step of anodizing a single-crystal silicon substrate in an electrolytic solution to form a porous silicon layer on a major surface of the single-crystal silicon substrate, the silicon film formation step of growing a single-crystal silicon film on the porous silicon layer, the removal step of bonding a first substrate obtained by oxidizing a surface of the single-crystal silicon film to a second substrate as a supporting substrate, and removing a single-crystal silicon portion from a lower surface side of the first substrate to expose the porous silicon layer, and the etching step of etching the exposed porous silicon layer to remove the porous silicon layer on the single-crystal silicon film, wherein in washing after the anodizing step, a time in which the first substrate is removed from the electrolytic solution and exposed to the air until washing is limited to a range in which the porous silicon layer is prevented from remaining on the single-crystal silicon film in the etching step.
An SOI substrate according to the first aspect of the present invention has the following structure.
There is provided an SOI substrate manufactured by the substrate processing method of any one of claims 1 to 5.
A substrate processing method according to the second aspect of the present invention has the following steps.
There is provided a substrate processing method comprising the anodizing step of anodizing a single-crystal silicon substrate in an electrolytic solution to form a porous silicon layer on a major surface of the single-crystal silicon substrate, the silicon film formation step of growing a single-crystal silicon film on the porous silicon layer, the removal step of bonding a first substrate obtained by oxidizing a surface of the single-crystal silicon film to a second substrate as a supporting substrate, and removing a single-crystal silicon portion from a lower surface side of the first substrate to expose the porous silicon layer, and the etching step of etching the exposed porous silicon layer to remove the porous silicon layer on the single-crystal silicon. film, wherein in washing after the anodizing step, a time in which the first substrate is removed from the electrolytic solution and exposed to the air until washing is set to be shorter than a time in which a compound produced by the electrolytic solution sticks to inner walls of pores formed by anodizing.
An SOI substrate according to the second aspect of the present invention has the following structure.
There is provided an SOI substrate manufactured by the substrate processing method of any one of claims 7 to 13.
A substrate processing method according to the third aspect of the present invention has the following steps.
There is provided a substrate processing method comprising the anodizing step of anodizing a single-crystal silicon substrate in an electrolytic solution to form a porous silicon layer on a major surface of the single-crystal silicon substrate, the silicon film formation step of growing a single-crystal silicon film on the porous silicon layer, the removal step of bonding a first substrate obtained by oxidizing a surface of the single-crystal silicon film to a second substrate as a supporting substrate, and removing a single-crystal silicon portion from a lower surface side of the first substrate to expose the porous silicon layer, and the etching step of etching the exposed porous silicon layer to remove the porous silicon layer on the single-crystal silicon film, wherein in washing after the anodizing step, a time in which the first substrate is removed from the electrolytic solution and exposed to the air until washing is limited to be not more than 3 min.
An SOI substrate according to the third aspect of the present invention has the following structure.
There is provided an SOI substrate manufactured by the substrate processing method of any one of claims 15 to 18.
A substrate processing apparatus according to the first aspect of the present invention has the following arrangement.
There is provided a substrate processing apparatus for performing the anodizing step of anodizing a single-crystal silicon substrate in an electrolytic solution to form a porous silicon layer on a major surface of the single-crystal silicon substrate, the silicon film formation step of growing a single-crystal silicon film on the porous silicon layer, the removal step of bonding a first substrate obtained by oxidizing a surface of the single-crystal silicon film to a second substrate as a supporting substrate, and removing a single-crystal silicon portion from a lower surface side of the first substrate to expose the porous silicon layer, and the etching step of etching the exposed porous silicon layer to remove the porous silicon layer on the single-crystal silicon film, wherein a plurality of first substrates can be processed at once in the anodizing step, and in washing after the anodizing step, all the first substrates can be transferred in a time in which each first substrate is removed from the electrolytic solution and exposed to the air until washing is limited to a range in which the porous silicon layer is prevented from remaining on the single-crystal silicon film in the etching step.
An SOI substrate according to the fourth aspect of the present invention has the following structure.
There is provided an SOI substrate manufactured by the substrate processing apparatus of any one of claims 20 to 24.
A substrate processing apparatus according to the second aspect of the present invention has the following arrangement.
There is provided a substrate processing apparatus for performing the anodizing step of anodizing a single-crystal silicon substrate in an electrolytic solution to form a porous silicon layer on a major surface of the single-crystal silicon substrate, the silicon film formation step of growing a single-crystal silicon film on the porous silicon layer, the removal step of bonding a first substrate obtained by oxidizing a surface of the single-crystal silicon film to a second substrate as a supporting substrate, and removing a single-crystal silicon portion from a lower surface side of the first substrate to expose the porous silicon layer, and the etching step of etching the exposed porous silicon layer to remove the porous silicon layer on the single-crystal silicon film, wherein a plurality of first substrates can be processed at once in the anodizing step, and in washing after the anodizing step, all the first substrates can be transferred in a time in which each first substrate is removed from the electrolytic solution and exposed to the air until washing is set to be shorter than a time in which a compound produced by the electrolytic solution sticks to inner walls of pores formed by anodizing.
An SOI substrate according to the fifth aspect of the present invention has the following structure.
There is provided an SOI substrate manufactured by the substrate processing apparatus of any one of claims 6 to 12.
A substrate processing apparatus according to the third aspect of the present invention has the following arrangement.
There is provided a substrate processing apparatus for performing the anodizing step of anodizing a single-crystal silicon substrate in an electrolytic solution to form a porous silicon layer on a major surface of the single-crystal silicon substrate, the silicon film formation step of growing a single-crystal silicon film on the porous silicon layer, the removal step of bonding a first substrate obtained by oxidizing a surface of the single-crystal silicon film to a second substrate as a supporting substrate, and removing a single-crystal silicon portion from a lower surface side of the first substrate to expose the porous silicon layer, and the etching step of etching the exposed porous silicon layer to remove the porous silicon layer on the single-crystal silicon film, wherein a plurality of first substrates can be processed at once in the anodizing step, and in washing after the anodizing step, all the first substrates can be transferred in a time in which each first substrate is removed from the electrolytic solution and exposed to the air until washing is not more than 3 min.
An SOI substrate according to the sixth aspect of the present invention has the following structure.
There is provided an SOI substrate manufactured by the substrate processing apparatus of any one of claims 13 to 16.
Other objects and advantages besides those discussed above shall be apparent to those skilled in the art from the description of a preferred embodiment of the invention which follows. In the description, reference is made to accompanying drawings, which form a part hereof, and which illustrate an example of the invention. Such example, however, is not exhaustive of the various embodiments of the invention, and therefore reference is made to the claims which follow the description for determining the scope of the invention.